`?include=...` query param

[amaury1093]

On the frontend, I need the territories, and their related PoliticalEntity's color.

@whirish proposed to return the color for requests on /territories. I solves my immediate problem, but it's not really future-proof.

Proposal:

• /territories?include=politicalentity, cf https://jsonapi.org/format/#fetching-includes

Notes:

• Other query params can also be added, like partial resources, i.e. ?fields=... to only return relevant fields, https://developers.google.com/tasks/performance#partial-response.
• The idea is to create a basic query language with query params. GraphQL would solve the problem, but we decided not to go that route.

[amaury1093]

Wrong repo, I need to sleep now...